Conventional internal combustion engine idle speed control systems make use of a proportional-integral-differential (PID) controller of air and a proportional controller of spark. The bandwidth of a PID controller is limited and, to obtain the required accuracy, idle speed control systems rely mainly on feed-forward airflow compensation. The typical feed-forward controller has tens of lookup tables.
The idle control systems, described in U.S. Pat. No. 5,463,993 to Livshits et al, in U.S. Pat. No. 5,421,302 to Livshits et al, and in U.S. Pat. No. 5,577,474 to Livshiz et al, each being assigned to the assignee of this application, and each being hereby incorporated herein by reference, enable significant improvement of idle speed control performance.
The controller described in U.S. Pat. No. 5,463,993 combines load rejection and steady state control but requires very qualified people to calibrate, must be defined for all environmental conditions, and requires accurate physical based models. In the implementation of the idle speed controllers, described in U.S. Pat. No. 5,463,993 and U.S. Pat. No. 5,421,302, oscillations of engine speed (RPM) were found in different altitudes under multiple park-drive transitions. Furthermore, the controller described in U.S. Pat. No. 5,463,993 does not have separation of mass airflow and throttle position control. This means that every change of the actuator will require a re-calibration of this controller for all altitudes.
The controller described in U.S. Pat. No. 5,577,474 incorporates the effects of slowly varying parameters into the idle speed control system but does not take into account initial operation at different altitudes, takes a long time to adapt the model to slowly varying variables, such as barometric pressure, and contains a multitude of lookup tables.
What is needed is a robust idle speed controller incorporating load rejection with barometric correction for different altitudes.